The Power of the FOPDT Model

If you’re a parent, then chances are you’ve encountered this dilemma: It’s the day after your son or daughter’s birthday and you’re now faced with the job of assembling gifts provided by friends and family.  You can either ‘wing it’ with the hope of constructing each toy quickly or you can hunker down and follow the manufacturer’s step-by-step instructions.  While ignoring the instructions and following your intuition seems like the faster option, most experienced parents know that those instructions represent a speedier solution which ultimately results in a happier child.

A similar choice routinely confronts process manufacturers when faced with tuning their PID-based control loops.  Whereas plugging in new tuning parameters based solely on intuition seems like the quickest solution, the use of a proven approach like use of the First Order Plus Dead-Time (FOPDT) dynamic model is the smarter choice.  The first option is widely referred to as “poke and hope” and isn’t much of a confidence booster.  The second option has been proven to provide the right answer and to do so faster.  In the end tuning the PID both quickly and correctly is the goal.

Following are some advantages of the FOPDT that are worth considering:

Universal

Whereas the PID is the dominant regulatory control technology, so too the FOPDT is the dominant process model used in industrial control.  Yes – higher order models are frequently used in advanced simulation exercises and in highly complex applications, but the FOPDT is the most common model used in the tuning of PID control loops.

Intuitive

The FOPDT model is highly intuitive and facilitates the manual tuning of PID controllers.  Calculation of the three model parameters – Process Gain, Process Time Constant, and Process Dead-Time – is straightforward and involves the use of only basic math skills.  What’s more, those same values are descriptive in the sense that they portray the associated control loop’s dynamics and are easy to understand.

Versatile

Whether you have PLCs from Schneider Electric and Rockwell Automation or a DCS like those from  Emerson, Honeywell, and Yokogawa, the FOPDT model’s versatility will support them all.  Once model parameters are calculated the values can be converted easily to tuning parameters using the corresponding OEM algorithm.

The FOPDT model is a powerful tool as it provides a consistent and effective means for tuning a production facility’s PID controllers.  If the goal is quick and accurate results, the FOPDT is the modeling tools for you and your plant.